Electric time delay apparatus



y 1960 c. J. ADAMS ETAL 2,935,621

ELECTRIC TIME DELAY APPARATUS Filed Feb. 12, 1958 INVENTORS CHARLES d. ADAMS, RAY E.COOPR BY ,1 {W

ATTORNEY United States Patent ELECTRIC TIME DELAY APPARATUS Charles J. Adams, Bloomingtou, and Ray E. Cooper, Normal, Ill., assignors to General Electric Company, a corporation of New York Application February 12, 1958, Serial No. 714,809

3 Claims. (Cl. 307-88) Our invention relates to electric control systems more particularly to devices for introducing a predetermined or adjustable time delay into an electrical circuit in response to an input signal. Such devices as are useful, for example, in electric control systems using logic type control elements or functions.

Time delay devices or industrial control applications are now generally of the motor operated type or the pneumatic relay type which utilize moving parts and moving contacts. In the pneumatic relay type, for example, an armature is magnetically actuated in response to a control signal to exert a force upon a flexible diaphragm which moves gradually as a result of a pneumatic or hydraulic escapement to open or close a pair of contacts after a predetermined time delay depending upon the rate of escapement. The moving parts and moving contacts of such devices are subject to wear and failure. Electronic type time delay devices, which do not require moving parts or contacts have not generally found acceptance for industrial application because of their fragility and because the time delays which they are ordinarily capable of introducing are too short, usually less than one second. For industrial application, the time delays desired are generally in the range of from one to sixty seconds.

Accordingly, an important object of the invention is to provide a completely static long-lived time delay device capable of introducing time delays between input and output signal of considerably greater than one second.

Among the difiicult problems involved in providing a static type time delay device for introducing such long time delays are those of accuracy, reliability, and compatibility with existing control systems. For example, the time delay introduced should not vary noticeably even though the power supplying voltages for the device vary considerably, for example i Moreover, the time delay introduced should preferably not depend upon the amplitude of a control signal, but only upon its presence or absence. Moreover, the time delay device should be capable of being energized by a small control signal, for example, less than 10 milliamperes. For industrial-appli cations it is also desirable that the time delay device be small, compact and composed of long-lived rugged components. Accordingly, other objects of the invention are to provide a reliable, accurate and compatible static type time delay device capable of introducing time delays between input and output signals greater than one second; which time delays are not dependent upon the amplitude of the input signal.

In general, in accord with the invention an electric time delay device is provided having a saturable reactor with a gate winding and a time delay control winding. The gate winding is connected in a load circuit and is designed to hold off core saturation for several power cycles. A time delay control winding is connected in a closed loop control circuit, and the amount of resistance in this closed loop circuit is selected or adjusted to provide the desired time delay before the load circuit of the reactor conducts. Means are provided for introducing a flux in the core of the reactor in opposition to the gate winding flux normally to inhibit operation of the load circuit.- Control means are also provided for reducing the magnitude of this inhibiting flux thereby to initiate a time delayed operation of the load circuit. For greater reliability and accuracy the load circuit is operated from a source of pulse power.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be easily understood by referring to the following description taken in connection with the accompanying drawing in which the sole figure is a schematic circuit diagram of a control system embodying one form of the invention.

Referring to the drawing, the invention is shown in connection with a control system utilizing an elemental logic function type control element 11, known as an or unit, and an electric delay device 12 operated from a pulse power supply 13 and a unidirectional voltage source 14. Power supply 13 is constructed to supply pulses of power to the load circuits of the or unit 11 and of the time delay device 12 as well as biasing and control voltages for the or unit 11. Unidirectional voltage source 14 provides a substantially constant reference voltage to the control circuit of the time delay device 12.

The control system illustrated in the drawing also includes a pair of control switches 8 and 9 connected in the control circuit of or unit 11 and a load device 10 connected in the output circuit of time delay device 12. The object of the control system is to deliver an output unidirectional current to load device 10 a predetermined or preadjusted time after either switch 8 or switch 9 is closed.

More specifically, power supply 13 contains a pair of input terminals 15 for connection to a source of alternating voltage, for example, 115 volts at a frequency of 60 cycles. A saturable reactor 16, the primary winding 17 of a saturable transformer 18 and a bridge type rectifier 36 are connected in series circuit across input terminals 15. Saturable transformer 18 has a center-tapped secondary winding 19 across which a thyrite voltage limiting disc element 20 is connected. The saturable reactor 16 and saturable transformer 18 cooperate to produce substantially rectangular wave pulses of short duration at the source frequency across the secondary winding 19 of the transformer. These pulses may, for example, have an amplitude of volts and a duration of 400 microseconds.

The center tap 21 of the secondary Winding 19 is connected to a grounded output terminal 22, and alternating voltage pulses appear between this grounded output terminal 22 and a pair of high voltage pulse output terminals 23 and 24 connected directly to opposite ends of the secondary winding 19.

These opposite ends of secondary winding 19 are also respectively connected through a pair of similarly poled rectifiers 25, 26 to a pulse output terminal 27. The voltage pulses appearing between terminals 22 and 27 are thus unidirectional rather than alternating in polarity.

The output terminals 28, 29 of bridge rectifier 36 are connected through a filter comprising capacitor 30 and inductance 31 across bias voltage supplying terminals 32, 33. Another bridge rectifier 34 is connected directly across input terminals 15 to supply unidirectional voltag across its output terminals 22 and 35.

0r unit 11 comprises a saturable reactor 40 having a pair of signal control windings 41 and 42, a bias control winding 43, a gate winding 44 and a feedback winding 45 all wound on a single loop saturable magnetic core 46. Control windings 41 and 42 are respectively connected in serieswith switches 8 and 9 and current limiting re.

sistors 47 and 48 across control voltage supplying terminals 22 and 35. Bias winding 43 is directly connected across bias voltage supplying terminals 32 and 33. Gate winding 44 and feedback winding 45 are connected in a series load or output circuit including a unidirectional conducting device 58, a current limiting resistance 51 and a pair of outpjut terminals 52 and 53. This load or output circuit is connected across unidirectional pulse power supplying terminals 22 and 27, the unidirectional conducting device 50 being polarized to pass the polarity of pulses delivered at terminals 22 and 27 by the power supply 13. A capacitor 55 is connected in parallel with feedback winding 45, resistance 51 and output terminals 52 and 53. Gate Winding 44, feedback winding 45 and signal control windings 41 and 42 are all wound and connected -to produce flux in the same direction within the saturable magnetic core 46 of reactor 40. Bias control winding 43, however, is wound and connected to produce flux in an opposite direction within core 46.

In the operation of or unit 11 the substantially con stant voltage supplied to bias control winding 43 from terminals 32 and 33 produces a biasing current in winding 43 causing flux in core 46 opposing that produced by gate winding 44 and feedback winding 45. The magnitude of this bias current is suflicient to hold core 46 in its negatively saturated condition such that only a small core magnetizing current flows through the load circuit as a result of the power pulses supplied thereto. The signal control windings 41 and 42 are arranged and connected to produce, upon closure of switches 8 or 9, flux in core 46 aiding the gate winding flux and opposing the flux pro duced by the bias current in winding 43. A signal current in either or both of these control windings, if sufficient to overcome the bias winding flux, drives the unit with snap action into its positively saturated state thereby permitting load current to flow. The capacitor 55 produces this snap action and also aids in filtering the power pulses supplied to a load connected between the output terminals 52 and 53 whereby the load receives a substantially constant or only slightly varying unidirectional output voltage. The unit moves from its nonconducting to conducting condition within one-half cycle of the supply frequency after either switch 8 or switch 9 is closed. This or unit 11 forms a portion of the subject matter described and claimed in application Serial Number 630,936, filed December 27, 1956 by Russell A. Brown and assigned to the present assignee.

The electric time delay device 12 of the present invention comprises another saturable reactor 60 having its output load circuit connected to receive alternating pulses of power from power supply 13 at its terminals 23 and 24. Saturable reactor 60 is preferably of the full wave type having a pair of saturable magnetic cores 61, 62 each having gate windings 63 and 64 respectively connected to the power receiving terminals 65 and 66 of the unit through similarly poled unidirectional conducting devices shown as rectifiers 67 and 68 respectively. Gate windings 63 and 64 have many more turns than conventional magnetic amplifiers and introduce a much longer magnetic flux time integral in the core which prevents core saturation for a short period of time dependent upon the frequency and shape of the power pulse. For example, gate windings 63 and 64 may have five times more turns than conventional magnetic amplifiers and introduce a firing delay equal to the time of power pulses at a repetition frequency of 120 pulses per second. Adjacent legs 69 and 70 of respective cores 61 and 62 have wound thereon a time delay control winding 71, a feedback winding 72, and a signal control Winding 73.

Time delay winding 71 is connected in a closed loop circuit including an adjustable resistor 74. The bottom ends of the gate windings 63 and 64 are connected in common to one side 75 of the feedback winding 72; the other side 76 of feedback winding 72 being connected in series with a current limiting resistance 77 and output load terminals 78 and 79 across which load 10 is connected. Gate windings 63 and 64 are thus connected in parallel with each other and in series with feedback winding 72, resistance 77 and output terminals 78 and 79. A capacitor 80 is connected in parallel with the feedback winding 72, resistance 77 and the output terminals 78 and 79. The output circuit is connected by means of a switch 82 either across alternating halves of the secondary winding 19 of transformer 18 when the switch 82 is in position A, or across the entire secondary winding 19 by means of additional unidirectional conducting devices such as rectifiers 83 and 84 when the switch 82 is in position B. Thus, with switch 82 in position A, the time delay device 12 receives pulses of power at its power receiving terminals 65 and 66 one-half the amplitude of those received with the switch 82 in position B. As indicated by arrows, gate windings 63 and 64 are wound and connected to produce flux in their respective cores 61 and 62 in the same direction as that produced therein by feedback winding 72.

Signal control winding 73 is connected in a control circuit which functions to introduce suflicient magnetic flux in cores 61 and 62 normally to inhibit operation of the load circuit of the time delay device and to reduce or remove this inhibiting flux upon the application of a control signal voltage or current from a suitable source, such as or unit 11. This control circuit comprises a unidirectional voltage dividing network including a voltage dropping resistance 85, a unidirectional conducting device 86, and a signal generating resistance 87 connected in series with the control winding 73. A voltage breakdown device, such as a silicon or germanium diode 88, having a known and sharp inverse voltage breakdown characteristic commonly called its Zener breakdown voltage, is connected in parallel with rectifier 86, control winding 73 and signal generating resistance 87. Such diodes are now generally available and are called Zener diodes.

The voltage dividing network of this control circuit is connected by means of control power receiving terminals 90 and 91 to a suitable source of substantially constant unidirectional Voltage, such as the output terminals 92, 93 of a separate unidirectional voltage source 14, as shown. The values of resistances 85 and S7 and the magnitude of the voltage source 14 are selected to produce a voltage at the junction 188 between diodes 86 and 88 which is less than the Zener breakdown voltage of Zener diode 88, while the ampere turns of signal control winding 73 are made sufiicient to inhibit saturation of core 61 and 62 under the influence of gate windings 63 and 64 in the absence of a control signal supplied across input or signal generating resistance 87.

Thus, in the absence of a control signal supplied to in put terminals 89, 91 of the electric time delay device 12, only a small core magnetizing current flows in the output load circuit including load 18 due to the inhibiting flux introduced by the current in signal control winding 73. However, when a control signal current of sufiicient mag nitude is supplied to the input terminals 89, 91 from the output terminals 52, 53 of or unit 11, the voltage both at the input terminal 89 and at the junction of diodes 86 and 88 increases above the Zener breakdown voltage of Zener diode 88 and this Zener diode 88 be comes conductive. The conduction of diode 88 short circuits the control winding circuit including diode 86 and the signal control winding 73 whereby the control winding 73 no longer introduces flux in cores 61 and 62 inhibiting the potential self-saturating effect due to load current in gate windings 63 and 64. Hence, in the absence of the control winding flux, each gate winding 63, 64 as well as the common feedback winding 72 introduce flux in the same direction in their respective cores 61 and 62 during alternate polarity pulse power periods supplied to the power terminals 65, 66 of time delay device 12. The flux introduced by the gate windings 63 and 64 and by the feedback winding 72 does not, however, im-

mediately drive the cores 61 and 62 into saturation because of the high inductance of gate windings 63 and 64, and because of the presence of closed loop time delay winding 71 which has a counter-electromotive force introduced therein producing flux in the cores 6'1 and 62 opposing the gate and feedback winding flux. This inductive effect of the time delay Winding 71 introduces a considerable delay in time before the cores 61 and 62 are driven into their respective saturation regions; this delay being dependent upon the magnitude of the reactance of winding 71 and upon the ratio of this reactance to the resistance in the closed loop circuit as well as upon the inductance of the gate windings 63 and 64 and the magnitude and duration of the current pulses passing through gate and feedback windings 63 and 64 and 72. Once the cores 61 and 62 begin to move into their saturation regions, the capacitor 80 in conjunction with the feedback winding 72 functions quickly to drive the cores deeply into saturation and permit load current to flow in the output circuit. Capacitor 80 also functions to convert the pulses of current passing through the gate windirrgs 63 and 64 into substantially unidirectional or sawtooth wave voltage applied across output terminals 78 and 79.

As mentioned above, the amount of time delay introduced between the input signal and the output current supplied to load 10 depends in part upon the ratio of reactance to resistance in the closed loop time delay winding circuit. The amount of time delay can thus be adjusted by varying the resistor 74 with the maximum time delay occurring when the resistor is completely shortcircuited. It has also been foundthat while the circuit is operable with sinusoidal power supplied across terminals 65 and 66, substantially greater time delays are achievable with better accuracy and reliability if a pulse power source such as power supply 13 is used. It has also been found that the amplitude of the power pulses supplied to terminals 65 and 66 does not greatly afiect the time delay introduced by the time delay winding circuit so that minor variations in power supply voltage do not affect the accuracy of the time delay setting. For example, with switch 82 in position A, the time delay introduced by device 12 for any given setting for resistor 74 is only slightly longer than that introduced with switch 82 in position B. However, the higher voltage position B has been found to be preferred for stability and satisfactory snap action in the output load circuit as well as to provide a greater output current.

A typical electrical time delay device 12 consists of magnetic cores 61 and 62 composed of rectangular highly saturable magnetic laminations having a cross-sectional area of 0.054 square inch. Gate windings 63 and 64 each have 1100 turns of 0.0045" diameter copper wire while feedback winding 72 has 200 turns of 0.0045" diameter copper wire. Signal control winding 73 has 700 turns of 0.0045" diameter copper wire and time delay winding 71 has 93 turns of 0.0126" diameter copper wire. Unidirectional conducting devices 67, 68, 83, 84 and 86 are all germanium rectifiers and Zener diode 88 is a germanium point contact type having a breakdown voltage of from 3.7 to 4.5 volts. Resistance 77 has 4000 ohms, resistance 85 has 12,000 ohms and resistance 87 has 820 ohms, while variable resistor 74 has a maximum resistance of 504 ohms. Capacitor has 2 microfarads capacity.

Although we have described our invention with a specific embodiment, many modifications can be made. For example, electric time delay device may be constructed or operated as a half wave device by utilizing only core 61 and its associated windings and circuitry and omitting core 62 and its associated circuitry.

It is to be understood, therefore, that we intend by the appended claims to cover all such modifications which fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric time delay device comprising a magnetically saturable core having a gate winding, a time delay winding and a control winding thereon, a closed loop circuit for said time delay winding, a load circuit for connection across a pulse power supply, said load circuit including said gate winding and a unidirectional conducting device, a voltage dividing network connected in series with said control winding, and a Zener diode connected to said voltage dividing network at least in parallel with said control winding.

2. A control system comprising a pulse power supply, a magnetically saturable core having a gate winding, a

time delay winding and a control winding thereon, a load circuit connected to receive power pulses from said power supply and including said gate winding and a unidirectional conducting device polarized to pass said power pulses, a closed loop circuit for said time delay winding, and control circuit means for abruptly changing a current in said control winding in response to a control signal to initiate a time delayed operation of said load circuit, said control circuit means including a voltage dividing network connected in series with said control winding and a Zener diode connected to said voltage dividing network in parallel at least with said control winding.

3. An electric time delay device comprising a pair of magnetically saturable cores each having a separate gate winding and having common time delay feedback and control windings, a closed loop circuit for said time delay winding including a variable resistance, a load circuit connection across a power supply, said load circuit including said gate winding, said feedback winding, a unidirectional conducting device and a pair of output terminals, a voltage dividing network connected in series with said control winding and a Zener diode connected to said voltage dividing network in parallel at least with said control winding.

References Cited in the file of this patent UNITED STATES PATENTS 

